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Structure Of A PPL-File

If you have used OpenHoldem in the past you will know that you have to answer several questions: Shall I go allin? Shall I raise? Shall I call? And if you answer all questions with no then OpenHoldem will fold. That is one approach and it clearly has some pros. But most poker-playing people and non-programers will find a different approach more easy: What shall I do in this situation? And that’s exactly how OpenPPL works.

Simple When Conditions With Actions

The most simple way to code a bot consists of a series of conditions followed by actions to be chosen.
WHEN HaveFlushDraw AND AmountToCall < 1/3 PotSize Call FORCE
These conditions are always evaluated top-down. Once the first condition is true, the appropriate action will be taken. Always! - so the order of programming matters. Let’s assume, that you want to call your flushdraws, but raise to 10bb your nut-flushdraws (expert-strategy 2012). Then you will have to write your commands in the following order:
WHEN HaveNutFlushDraw RaiseTo 10 FORCE
WHEN HaveFlushDraw Call FORCE
Do it the other way and your nut-flush-draw would trigger the rule for normal flush-draws. A call would be the result. As a consequence of this top-down-evaluation we recommend you deal with:
  • strong hands first, special cases first
  • weak hands last, general cases last
The bot simply does not know if one rule is “more special” or “more important” — you have to tell it by your coding order.
If you wonder about the keyword force: it was inherited from Shanky-PPL and means, that it overwrites the default bot (without Force). Though we don’t provide a default bot and don’t think, that user-defined actions should be ignored if they lack the FORCE, we kept this keyword to stay compatible and because it is nice to read (syntactical sugar).

Open-Ended When Conditions

Programming your bot with when-conditions alone will — in principle --- do the job, but there will be lots of situations that are very similar.
WHEN hand$AT AND StillToAct = 2 AND Raises = 1 AND AmountToCall <= 4 RaisePot FORCE
WHEN hand$AT AND StillToAct = 2 AND Raises = 1 AND AmountToCall > 4  Fold FORCE
WHEN hand$AT AND StillToAct = 2 AND Raises = 2 ...
Here one part of the condition gets repeated:
WHEN hand$AT AND StillToAct = 2
For more sophisticated profiles this would be lots of code to write, lots of code to evaluate and a true nightmare to change once you want to improve it. So OpenPPL provides two kinds of conditions: top-level conditions without actions (called “open-ended when-conditions”) and simple “when conditions with actions” like explained above.
Once the first open-ended-when-condition is located all following “normal” when-conditions are bound to that condition and only evaluated when the open-ended when-condition is true. So you could rewrite the example above like that:
WHEN hand$AT AND StillToAct = 2
    WHEN Raises = 1 AND AmountToCall <= 4 RaisePot FORCE
    WHEN Raises = 1 AND AmountToCall > 4 Fold FORCE
    WHEN Raises = 2 ...
WHEN hand$A9 AND StillToAct = 2
Each open-ended when-condition is active until the next open-ended when-condition is found. In the example above:
WHEN hand$A9 AND StillToAct = 2
To terminate all your open-ended when-conditions just write:
When Others
    When Others Fold Force
Coding this way makes your code smaller, more easy to read and more easy to change. However: some people would like to take code-structuring to extremes and use multiple nested open-ended when-conditions like below:
WHEN hand$AT
    WHEN StillToAct = 2
        WHEN Raises = 1
            WHEN (AmountToCall <= 4) RaisePot FORCE
            WHEN (AmountToCall > 4) Fold FORCE
        WHEN Raises = 2
In principle this is a good idea, but it does not work. Simply because there is no way to tell, where one open-ended when-condition ends and where the next one starts. So the semantics would be completely undefined (it is in fact not, but it is for sure not what you want). Sure you could argue about indentation, but spaces have no meaning in most programming languages (except good old Fortran 77) and everybody does it differently. So let’s restate: There is at most one level of open-ended when-conditions (without action), each one bound to a sequence of when-conditions with actions. If you want to structure your code even more (a very good idea!) then we recommend to look at the chapter “Building Symbols On Your Own”.

Controlflow of Open-Ended When-Conditions

figure images/when_conditions_control_flow.png

Structure Of A PPL-File

Once you understand how when-conditions work, programming your first bot becomes easy and straightforward: you just have to provide a sequence of when-conditions for Preflop, Flop, Turn and River. These 4 main code-sections are named f$preflop..f$river, because that’s how user-defined OpenHoldem symbols get named and from a technical point of view these code-sections are functions.
    // This is a comment
    // Your code belongs here.
    WHEN hand$AA RaiseMax FORCE	
    WHEN hand$KK ...
    WHEN Others Fold FORCE

Unspecified Return Values

People who create complete profiles usually add
WHEN Others
   WHEN Others Fold FORCE
to the end of every code-section. But it does not hurt if you don’t so. If no condition matches the situation OpenHoldem will automatically continue to evaluate the built-in default-not (Gecko). If no default-bot is present (you may safely delete it) then OpenHoldem will evaluate functions without a return-value to zero, which is also the encoding for false, and also for check/fold.

More Advanced Coding

Coding sequences of when-conditions is very easy and intuitive, however there is one big disadvantage: poker is a somewhat complex game and there are countless situations to consider. So these code-blocks can become rather large — too large for a sane human mind. But of course there is a solution: OpenPPL supports structured coding, namely:
  • user-defined hand-lists
  • user-defined symbols, i.e. named functions, that get defined once and can be used at multiple places.
Both of them are very useful, but a little bit “advanced” and not standard Shanky-PPL. So we discuss them in later chapters of this manual.